1. Field of the Invention
The invention relates to a torsional vibration damping device, in particular for rotating clutch disks which interact with internal combustion engines, having two coaxial cover disks, which can be rotated relative to each other within a fixed angular range relative to an internally located part and which accommodate between them a number of circumferentially directed torsion springs, the cover disks being loaded in the axial direction by a spring force in the opposite direction and being fixed by axial distance pieces, which are connected to a cover plate at each end, the cover disks and the internally located part being arranged on a hub furnished with splines.
2. Description of the Related Art
Vibrations occur in almost all drive trains because of internal or external excitations. Particularly when associated with internal combustion engines, the vibrations caused in principle lead to undesired phenomena. In addition to strength problems, they mainly cause noises which can be noticeable in the gearbox as gearbox clatter and as jolting in the drive train. For this reason, clutch disks and, for example, twin-mass flywheels also are provided with torsional vibration damping devices which essentially operate by a hub disk coaxially arranged between two cover plates being relatively displaceable within a certain angular range against the force of torsion springs.
A prior art torsional damping device is, for example, known from German reference DE 196 13 574 A1. The prior art torsional vibration damper disclosed in this publication has at least three spring stages dimensioned for different torque ranges of the torque to be transmitted between an input component and an output component. Each of the spring stages has a graduated effectiveness in associated ranges of the relative rotational angle between the input component and the output component. Therefore, a three-stage prior art device has low, medium, and high stages respectively corresponding to an initial damper dimensioned for idling operation, a crawling speed damper dimensioned for low speed operation, and an under-load damper dimensioned for under-load operation. Each stage has an initial torque and a final torque. The initial torque of the medium stage is smaller than the final torque of the low stage. Similarly, the initial torque of the high stage is smaller than the final torque of the medium stage. The initial damper and the crawling speed damper are axially moveable via splines in the disk parts guiding the damper springs but are connected to the output part with rotational clearance corresponding to the operating ranges of the damper. Friction devices associated with the individual damper stages can be accommodated between the individual disk parts. The hub, which can be placed on the input shaft of a gearbox, includes splines which act in the radial direction and on which the inner part of the torsional vibration damping device is placed. The two cover plates are placed on the hub to both sides of the splines and are supported against the splines. For this purpose, drive disks are provided coaxially between the two cover plates and the cover plates are supported against the drive disks, a plate spring being provided between one drive disk and one cover plate and a friction ring being provided between the other drive disk and the other cover plate. The cover plates, which extend in the radially inward direction beyond the splines of the hub, are axially supported against the spline teeth of the hub and therefore axially secure the hub.
Corresponding installation space is required to accommodate the plate spring and the friction ring in the axial direction so that the clutch disk, which contains the torsional vibration damping device, has a correspondingly wide structure. Since the plate spring is supported between the cover plate and the drive disk, the frictional relationships present are, in addition, not always reproducible because, as is known, steel-to-steel contact represents a critical friction pairing.
Modern vehicles are increasingly equipped with high-torque engines so that the clutch disk has to have correspondingly larger dimensions for transmitting the corresponding torque. The increase in the use of higher-torque engines permits the engine to perform a larger number of auxiliary functions. Accordingly, there is an associated increase in the amount and variety of equipment installed in vehicles, thereby providing less and less space available for the individual components in the engine compartment of a vehicle. Modern vehicle units therefore demand the most compact possible construction. The known torsional vibration damping device, whose structure is quite wide in the radially inner region, can no longer satisfy the functionality demanded in many cases.